In the prior art, known valves supply hydraulic oil from a pump to a priority flow circuit at a predetermined flow rate and supply the remaining oil to a surplus flow circuit. For example, Japanese Laid-Open Patent Publication No. 60-159407 describes a valve that distributes fluid supplied from a pump to a pilot circuit, which functions as a flow priority circuit, and an auxiliary circuit, which functions as a surplus flow circuit. The valve includes a spool hole and a spool accommodated in the spool hole. The spool hole, which functions as a fluid chamber, communicates with the pilot circuit, the auxiliary circuit, and a supply flow path. The fluid supplied from the pump flows through supply flow path to the spool hole. The supply flow path has three openings that communicate with the spool hole. This distributes the fluid from the supply flow path to two systems, that is, the surplus flow circuit and the flow priority circuit. A priority restriction for restricting the flow to the priority flow circuit and a surplus restriction for restricting the flow to the surplus flow circuit is formed between the spool and the wall surface of the spool hole.
In the valve of the above publication, fluid force from the fluid entering the priority flow circuit and urging the spool in the axial direction of the spool is balanced with fluid force of the fluid entering the auxiliary circuit and urging the spool in the axial direction of the spool. However, when the priority restriction formed between the spool and the wall surface of the spool hole causes a large pressure drop, the fluid forces are imbalanced. This increases the force applied in a direction from the priority restriction to the auxiliary restriction, that is, toward the pilot circuit (the direction indicated by arrow 97 in FIG. 2 of the above publication). In the valve, therefore, a circuit, which includes a pilot port, a check valve, and an orifice, are formed to apply force, which offsets the spool urging force produced by fluid force, to one end of the spool.
However, with the valve of the above publication, a more complex circuit structure becomes necessary to optimally offset the spool urging force with fluid force.